As violent crime nationally slows in growth or declines, the United States is facing a dramatic — but hardly noticed — increase in murders by and of young African-American men, a Northeastern University study released today reports.

Between 2002 and 2007, the number of black male juveniles murdered nationally increased by 31 percent and the number of black perpetrators by 43 percent. The increases were even greater, the report said, when guns were used as weapons.

Focusing on the period between 2000-01 and 2006-07, the study found Houston at the top of a list of 28 U.S. cities, with a 139 percent increase in the number of young African-Americans suspected in killings.

In 2006-07, 129 young black men were murdered in the city, up from 42 in 2000-01.

Those increases came as homicides by and of young white men slowed or declined. In Houston, the number of white offenders dropped by 10 percent. Nationally, FBI statistics showed murder decreased 1.3 percent in 2007 from the previous year.

"I don't want to suggest that this is an epidemic, a crisis situation," said study co-author James Fox, professor of criminal justice and law, policy and society at the university in Boston. "But it's absolutely a growing concern, not a one-year blip."

Fox and his associate, criminologist Marc Swatt, argued in the report that the increases occurred as the federal government cut support for community policing and intervention programs put in place to combat a rise in gang violence in the 1990s.

Though current violence falls short of levels in the '90s, the report's authors called for renewal of government support for intervention. "Let this small upturn serve as a thunderous wake-up call that crime prevention needs to be a priority again," they wrote.

"Kids can't wait, and crime doesn't wait," Fox said. "There is a significant need here — a large group of kids with inadequate, inferior education and a ready access to guns. A teenager with a gun in his hand is a dangerous individual."

Houston community activist Quanell X called the study a "blanket indictment of the city and government officials in the city and a greater indictment of ministers and political leaders of the African-American community."

He called for a citywide black leadership summit to find ways to end the violence.

"Until African-American leaders, both spiritual and political, male and female, can get into that room and check their egos at the door and say, 'To hell with party politics,' and walk out of that room with a plan all of us can have a part in," the killings will continue, he said.

Shape Community Center's Deloyd Parker questioned the way the study was conducted. "When they say 'offender,' does that mean someone who's charged with a crime or been convicted?" he said. "Sometimes even being convicted doesn't mean you're actually guilty."

Fox responded that the number of young offenders was calculated from instances in which "police knew who did the crime" and through a statistical process called "imputation."

Imputation, used when crimes have not been solved, essentially intuits the offender's race from location of the killing and other circumstances of the crime.

"The whole foundation of the study is in question," Parker charged. " ... He's going to have to do a little better homework for me to even mess with this."